1. Field of the Invention
The present invention relates to a servomotor controller for driving actuators possessing electric motors. More particularly, the invention relates to a servomotor controller which can perform serial data communication between a superordinate device (control unit or the like).
The present invention also relates to a servomotor controller having a data communication function, in particular, to a servomotor controller capable of releasing a state that feedback control is stopped for preventing hunting, by a command from a superordinate device, and the like.
2. Related Art Statement
(1) Problem 1 to be Solved
With respect to various doors arranged in an air-conditioning unit for an automobile, there has been formerly known an air-conditioning system which comprises respective actuators of the same kind each including a motor for driving the door, a position detector for detecting a present position of the door as a voltage and a control unit for controlling the motor based on given target positional data and outputs from the position detector, wherein these actuators of the same kind are totally controlled by a controller through serial communication. In the automobile air-conditioning system thus constructed, the controller counts the number of times of state changes of target position-reaching signals received from the actuator, and prevents long-time hunting of the actuator by transmitting a signal for stopping the actuator when the counted value becomes a predetermined value or above (See JP-A-8-332832).
Even though driving of the motor is stopped when the present position conforms to the target position, the present position exceeds the target position by overrun with inertia, and the control circuit manages to match the present position with the target position by reversely rotating the motor. By repeating this, vibration phenomenon so-called hunting is occurred, resulting in noise generation depending upon an application system. In order to prevent this hunting, a conventional method has been taken, which sets a range beyond the overrunning with respect to the target position as hysteresis, and stops the rotation of the motor when the present position exists within the hysteresis (See JP-A-8-186881).
There has been also known a conventional positioning device. In the positioning device for carrying out feedback control of a motor in order to stop an object to be controlled (hereinafter referred to as control object) in a target position, wherein the device outputs a driving-permitting signal to a driving circuit when signals beyond a stop range are continuously generated for a predetermined time or more, and by continuing the outputting of the driving-permitting signal during a predetermined time period from the beginning of the outputting, the driving circuit does not repeat ON and OFF operations even when an outside noise enters a present position signal or the like (See JP-A-9-134218).
Much load (processing amount) of the controller side is included in the methods which prevent hunting by observing the state changes of the target position-reaching signals received from the actuators. Moreover, when the hunting occurs, the actuators may carry on unnecessary operations and unnecessary power consumption until the stop signal is supplied from the controller side.
In the method which stops the rotation of the motor after the present position falls within the target range, when the motor is stopped before or after the target position through the noise entering the position detecting signal, a superordinate device (controller or the like) has to take a complicated handling method such as transmitting a dummy target value which is well off the target value for restarting the actuator, and then transmitting an appropriate target value again.
If the driving-permitting signal is output in order to avoid influence of the outside noise when the signals falling outside the stop range are continued for a predetermined time or more, a response becomes slow when changing the target value. On the other hand, if the outputs of the driving-permitting signals are continued for a predetermined time, the possibility of overrunning increases.
(2) Problem 2 to be Solved
There has been heretofore known an actuator which includes a serial data communicating section to receive target value data transmitted from a control unit and control the rotation of a motor so that an output from a rotating angle detector may be in conformity with a target value. The control unit feeds only the target value data to the actuator, and the motor is controlled from a side of the actuator alone. Thus, the control unit cannot recognize whether the motor normally operates or not.
Thus, the control unit transmits a diagnosis command to the actuator. When the actuator receives such a diagnosis command, an A/D converter converts an output from a rotary angle detector to a digital value, which is transmitted in the form of a given format via a transmitting circuit after being coded with an encoder. A data processing section of the control unit receives this datum via a receiving circuit and a decoder, so that a present value of the rotation angle of the motor can be known. Instead of transmitting a special command called the diagnosis command on diagnosing, it may be that every time the control unit transmits an ordinary target value, the actuator, which receives it, returns a present value datum.
However, the actuator requires the A/D converter for converting the outputs from the rotation angle detector to the digital values and the encoder for encoding the converted outputs so as to diagnose any trouble. On the other hand, the control unit requires the decoder for decoding the encoded data from the actuator. Consequently, the scale of the circuit becomes bulky.
Under the circumstances, the actuator is provided with a controlling termination detector which is adapted to detect the termination of controlling the rotation angle of the motor when the present value of the rotation angle of the motor reaches almost the target value as well as a transmitting unit which adds, to the controlling data, controlling termination data thereof and which outputs the added resultant to a communicating line when the receiver receives control data from the control unit. By this construction, the size of a circuit required for the self diagnosis is reduced, and a transmitting frame becomes shorter. Since the self diagnosis is performed by the transmitted data only, the number of communications per unit time can be increased to improve response performance (See JP-A 8-102979).
With respect to doors arranged in an air-conditioning unit, there are provided respective actuators of the same kind each including a motor for driving the door, a position detector for detecting a present position of the door as a voltage and a control circuit for controlling the motor based on given target positional data and outputs from the position detector and these actuators of the same kind are totally controlled by a controller through dual-directional serial communication. In an automobile air-conditioning system thus constructed, it is known that after the controller transmits a given door positional information for inspection to a target one of the plural actuators, the controller detects if it received a target position-reaching signal from the target actuator, and then makes a displaying section display a detection result (See JP-A-9-99729).
In the automobile air-conditioning apparatus for controlling each of the actuators with the one line-type serial communication, it is known that communication signals (serial signals) transmitted and received through the communication line include actuator-discriminating information (address), driving/stopping signals for the motor, target stopping position signals (target position data) and error detection information (parity data) as information data from the auto amplifier (controller) to the actuator as well as the target position-reaching information as the information data from the actuator to the auto amplifier (controller) (See JP-A9-109662, paragraph 0030).
According to the system in which the target position-reaching information is transmitted from the actuator side to the control unit as the superordinate device, the amount of the data in the serial communication may be small, but as a matter of course, the system can make only self diagnosis as to whether the door reaches the target position. Therefore, it is difficult from the side of the control unit to predict any abnormality on the side of the actuators. For example, even if any actuator is in an overloaded state, such cannot be predict or detected.
As described in JP-A 8-102979, when a diagnosis command is transmitted from the control unit to the actuator and the actuator having received the diagnosis command returns the present positional data to the control unit, the controller can effect various diagnosis grasp the operation state of the actuator side and effect various diagnoses. However, in order to further add a diagnosis commanding menu to the existing system having no such a diagnosis commanding menu, a circuit and a program must be added to decode and execute the diagnosis command. Therefore, it may be necessary to newly construct a custom IC, etc. constituting a main portion of the actuator, so that it is often difficult to readily cope with the adoption of the diagnosis commanding menu.
If the actuator returns the present positional data to the control unit every time when the controller transmits the ordinary target value data, the target value data must be transmitted in obtaining the present positional data, which undesirably results in an increased amount of the communication data.
In order to diagnose the operation of the actuator side at the side of the control unit, the contents of the diagnosis can be enriched if not only the present positional data but also information on the rotating direction of the motor and the driven/stopped state of the motor.